title: The concurrent effects of strike pattern and ground-contact time on running economy.
abstract: OBJECTIVE
  Running economy is a key determinant of endurance performance, and understanding the biomechanical factors that affect it is of great theoretical and applied interest. This study aimed to analyse how the ground-contact time and strike pattern used by competitive runners concurrently affect running economy.
  
  
  METHODS
  Cross-sectional.
  
  
  METHODS
  Fourteen sub-elite male competitive distance runners completed a 6-min submaximal running trial at 14kmh(-1) on an outdoor track using their habitual strike pattern (n=7 rearfoot strikers: average age, 25.3 years old (SD=2.4); average weight, 64.7kg (SD=5.6); average height, 175.3cm (SD=5.2); n=7 midfoot strikers: average age, 25.0 years old (SD=2.8); average weight, 69.6kg (SD=4.0); average height, 180.1cm (SD=5.1). During the run, the oxygen uptake and ground-contact time were measured.
  
  
  RESULTS
  Midfoot strikers showed a significantly shorter (p=0.015) mean contact time (0.228s (SD=0.009)) compared with rearfoot strikers (0.242s (SD=0.010)). Conversely, there was no significant difference (p>0.05) between the groups with respect to mean oxygen uptake (midfoot strikers: 48.4mlmin(-1)kg(-1) (SD=5.3); rearfoot strikers: 49.8mlmin(-1)kg(-1) (SD=6.4)). Linear modelling analysis showed that the effect of contact time on running economy was very similar in the two groups, with a 1ms longer contact time involving an approximately 0.51mlmin(-1)kg(-1) lower oxygen uptake. In contrast, when controlling for contact time, midfoot striking involved an approximately 8.7mlmin(-1)kg(-1) lower oxygen uptake compared with rearfoot striking.
  
  
  CONCLUSIONS
  When adjusting the foot-ground contact biomechanics of a runner with the aim of maximising running economy, a trade-off between a midfoot strike and a long contact time must be pursued.
authors.affiliation: Department of Biomedical and Neuromotor Sciences, School of Pharmacy, Biotechnology and Sport Science, University of Bologna, Italy. Electronic address: rocco.dimichele@unibo.it.
authors.forename: Rocco
authors.initials: R
authors.lastname: Di Michele
authors.affiliation: Department of Biomedical and Neuromotor Sciences, School of Pharmacy, Biotechnology and Sport Science, University of Bologna, Italy.
authors.forename: Franco
authors.initials: F
authors.lastname: Merni
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D005080:Exercise Test; D005528:Foot / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D012420:Running / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: Athletic performance; Biomechanics; Distance running; Oxygen consumption; Physical endurance